The impact of all the various threats on Mexican cacti and other succulents depends on the population characteristics of individual species. The majority of Mexican endangered cacti occur in small, disjunct populations, primarily in arid and semi-arid regions of the country, and a significant proportion of them are represented only by one or a few populations. Most of these species have a combination of biological and ecological attributes making them extremely vulnerable to any form of disturbance. These plants usually have slow growth rates, long life cycles, and the recruitment of new individuals in the population is extremely low. These inherent characteristics, along with the peculiar biogeographical patterns of these plants, determine a slow demographic response of the populations after disturbance. Unfortunately, accurate plant population information is generally not available and so it is often difficult to evaluate the precise degree of threat to individual species.
Various preliminary studies of the conservation status of Mexican succulents have been carried out over the past fifteen years. The Threatened Plants Committee (TPC) of IUCN undertook a survey of the conservation status of Mexican Cactaceae in the early 1980s mainly by correspondence with experts in Mexico and elsewhere. IUCN categories of threat were applied to all Mexican species and this formed the basis for the data on Mexican cacti held by WCMC. Data holdings at WCMC have recently been revised by harmonising with the CITES
* SEDUE (Secretary of Urban Development and Ecology) was superceded in the area of ecology, in the early 1990s, by SEDESOL (Secretary of Social Development). Under the new President, Ernesto Zedillo, SEDESOL was further refined to SEMARNAP (Secretary of the Environment, Natural Resources and Fish). Within that organisation, INE (National Institute of Ecology) is the institution most actively involved with threatened species and collecting permits.
Cactaceae Checklist (Hunt 1992) and information on threatened Mexican cacti and other succulents published by SEDESOL and subsequently SEMARNAP".
Concern about the situation in the wild of Mexican CITES Appendix I cacti led to the field survey work conducted by members of the SSC Group and Mexican conservation trainees from 1986 to 1988, funded by WWF-US. The results of this field work (Sánchez-Mejorada et al. 1986; Anderson 1990; and Anderson et al. 1994) confirmed the conservation status of a range of 52 rare and threatened species.
More recently, a newly formed group working at the Institute of Biology, UNAM, has centred its research activities on the study of the biogeographical patterns of the Mexican endangered species, particularly those growing in the Chihuahuan Desert Region (Hernandez and Godinez 1994; Hernandez and Barcenas 1994). Over the past few years this same group has assembled a database of herbarium collections from North and Central American Cactaceae containing so far (September 1994) over 9500 records from 37 Mexican, USA, and European herbaria (Hernandez et al. 1993). This is the largest available database containing geographical data on cacti species, and is proving invaluable to determine the areas of species concentration of endangered cacti in Mexico.
It has been estimated (Hernandez and Godinez 1994) that 73 per cent of the genera and 78 per cent of the species of cacti occurring in Mexico are endemic, and that 35 per cent (197 species) are somewhat endangered. In absolute terms, the country possesses the highest numbers
Mexican cactus and plant collector with Pelecyphora strobiliformis, Tamaulipas, Mexico.
Pachycereuspringlei, Desert Botanical Garden, Arizona.
of endemic and endangered cacti, comparing with other countries such as Chile, Ecuador, Cuba, and Brazil which also have highly significant proportions of endemic and endangered species.
Currently field surveys to assess the status of Mexican cacti are being undertaken by scientists from various botanical gardens and universities within Mexico. Botanists at UNAM are, for example, working on ecological and population studies in the Chihuahuan Desert area in the Tehuacan-Cuicatlan Valley and have been studying the conservation status of cacti in the State of Queretaro for over ten years. At a recent conference on population studies held at Can Te, A.C. in San Miguel de Allende, Guanajuato presentations were given on work in progress by researchers at the Universidad Autónoma de Tamaulipas, the Centro de Investigaciones Biologicas de Baja California Sur and the ITESM, Campus Queretaro. Can Te, A.C. is continuing to work with these institutions and others to pull together the diverse information available. A comprehensive program of detailed population studies is urgently needed to build on the work already in progress. It is clear that this must be coordinated and implemented locally.
Few detailed studies have been made of the long-term fluctuations of cacti and other succulent plant populations in habitat. These are necessary to understand the natural behaviour of populations and the reasons for their rarity, and, via comparative studies, to assess the basis of their vulnerability. Can Te, A.C. started such investigations in 1991 and currently has 50 ongoing studies with others in preparation. Concomitant with further population studies, additional long term studies can and need to be initiated.
A CITES-financed project is currently in progress to carry out population studies on Mexican cacti and to evaluate the impact of legal and illegal trade on wild populations of these species. The work is being carried out by Can Te, A.C. and the Desert Botanical Garden, Phoenix, with the assistance of several local botanic institutions.
Information on the conservation status of Mexican Agavaceae is included in Annex 1. A list of threatened Mexican cacti and other succulents as prepared by SEMARNAP is given in Annex 11. The cactus information within that list is based on Hernandez and Godinez (1994) which modified Hunt's (1992) CITES Cactaceae Checklist.
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